Combine the port, sugar, cinnamon, cloves, lemon zest, and orange zest in a small nonreactive pot. Cut the vanilla bean in half lengthwise, scrape out the seeds, and add both the pod and the seeds to the pot. Heat until the sugar dissolves. Peel the pears and core them through the blossom end with a melon baller, leaving the stem end intact. Add the pears to the pot and drape them with a piece of cheesecloth. Bring to a boil and simmer for 18 to 20 minutes, or until tender. Using a slotted spoon, remove the pears to a plate. Boil the poaching liquid another 14 to 16 minutes, or until thickened and slightly syrupy. Stir in the lemon juice, strain through a fine mesh sieve, and let cool slightly. Arrange the pears on individual plates, drizzle with the sauce, and serve immediately.

Serves 6. May be served warm or at room temperature. Perfect with gingersnap cookies. To obtain strips of zest from a lemon and an orange, simply use a vegetable peeler. The cheesecloth will keep the pears completely submerged beneath the poaching liquid so that they cook and color evenly. Leftover sauce, should you have any, is fantastic over ice cream.